1. Field of the Invention
The present invention relates to a converter for receiving a satellite signal with a dual frequency band. More specifically, the present invention relates to a converter of an antenna for satellite broadcasting or communication and to an input waveguide portion of a converter receiving two circularly polarized waves (right-hand and left-hand circularly polarized waves) with two separate frequency bands such as Ku and Ka bands.
2. Description of the Background Art
Parabolic antennas are mostly used as antennas for satellite broadcasting or communication. A parabolic antenna includes a reflecting mirror facing a satellite, a primary radiator receiving radiowaves collected by the reflecting mirror, and a converter for performing amplification and frequency conversion on the radiowaves received by the primary radiator. Many of the recent small-sized parabolic antennas have a primary radiator and a converter which are integrated together.
In these days, Ku band (frequencies extending from about 10.7 to 14.5 GHz) is mainly used for satellite broadcasting or communication. However, especially in these countries such as United States, frequency bands of Ku band are becoming densely allocated. In addition, for high-definition television broadcast requiring a wide frequency band or for data communication required to operate at high speed with large capacity, use of Ka band (at a higher frequency of about 20 GHz) is planned.
The Ku and Ka bands coexist, so that the demand of receiving radiowaves with two frequency bands by one antenna and converter naturally arises. Conventional techniques related to a primary radiator for a dual frequency band include use of a primary radiator which handles both C band (at a frequency of about 4 GHz) and Ku band.
FIG. 20 is a diagram showing an interior of a waveguide of a conventional primary radiator for a dual frequency band, and FIG. 21 is a cross sectional view thereof. The primary radiator for dual frequency band shown in FIGS. 20 and 21 is disclosed in Japanese Utility Model Laying-Open No. 63-33206.
Referring to FIGS. 20 and 21, the primary radiator for dual frequency band is a circular waveguide (a coaxial waveguide) of a dual structure where a signal with a low frequency band f1 (hereinafter referred to as f1) is transmitted through an outer waveguide 201 and a signal with a high frequency band f2 (hereinafter referred to as f2) is transmitted through an inner waveguide 211. The primary radiator for dual frequency band receives circularly polarized waves. 90xc2x0 phasers 202 and 212, respectively for f1 and f2 signals, are provided inside outer waveguide 201 and inner waveguide 211.
Referring to FIG. 20, circularly polarized wave signal f1 from the right side is transmitted through outer waveguide 201, converted to a linearly polarized wave signal by 90xc2x0 phaser 202, and further transmitted to a rectangular branching waveguide 204 through a step converter 203 from outer waveguide 201.
Circularly polarized wave signal f2 is transmitted through inner waveguide 211 and converted by a linearly polarized wave signal by 90xc2x0 phaser 212. Linearly polarized wave signal f2 is received by a probe 213 in the waveguide and transmitted to a converter circuit for f2 (not shown) through a coaxial line 214.
As shown in FIG. 21, coaxial line 214 includes a middle conductor 215, outer conductors 217 outside thereof, and electrical inductors 216 between middle conductor 215 and outer conductors 217. Middle conductor 215 is electrically connected to probe 213. Outer conductors 217 are electrically connected to inner waveguide 211 and outer waveguide 201, respectively.
It is noted that signal f1 which has been converted to the linearly polarized wave is also transmitted to a converter circuit for f1 through a probe (not shown) from branching waveguide 204.
As shown in FIG. 20, the conventional primary radiator for dual frequency band is of course applicable to Ku and Ka bands, but can receive only one polarized wave (right-hand or left-hand circularly polarized wave) with one frequency band. This is because only one coaxial line for f2 can be arranged. If two polarized waves (right-hand and left-hand circularly polarized waves) are to be received with frequency band f2, in addition to a horizontally arranged probe 213 and coaxial line 214, one more probe and coaxial line must be arranged in an orthogonal direction (a perpendicular direction in FIG. 20). However, with such a structure, two orthogonal coaxial lines for f2 pass through outer waveguide 201 and short-circuiting is caused by two orthogonal outer conductors. As a result, any polarized wave cannot pass through outer waveguide 201.
The only polarized wave that allows signal f1 to pass through outer waveguide 201 is that which is orthogonal to the coaxial line for f2. Thus, only one polarized wave can be received with each of frequency bands of f1 and f2. As frequency bands for satellite broadcasting or communication become more densely allocated as in recent years, a communication means which utilizes two polarized waves within the same frequency band becomes popular for the purpose of effectively utilizing radial waves. Therefore, a primary radiator or converter which can receive only one polarized wave with one frequency band would not be sufficient.
Therefore, a main object of the present invention is to provide a converter for receiving a satellite signal with a dual frequency band capable of implementing a primary radiator receiving two different circularly polarized waves with respective frequency bands in a converter receiving two frequency bands.
The present invention is a converter for receiving a satellite signal with a dual frequency band having a waveguide of a dual structure with a first waveguide and a second waveguide coaxially arranged therein. A plurality of sections are arranged between the first and second waveguides and one section is arranged inside the second waveguide.
Another aspect of the present invention is a converter for receiving a satellite signal with a dual frequency band having a waveguide of a dual structure with a first waveguide and a second waveguide coaxially arranged therein. First and second sections are arranged between the first and second waveguides, and a third section is arranged inside the second waveguide.
According to the present invention, a primary radiator of receiving two different circularly polarized waves (right-hand and left-hand circularly polarized waves) of respective frequency bands can be implemented.
Preferably, the first and second waveguides have a square or circular shape.
Preferably, the first, second and third sections are arranged in parallel with the axial direction.
Preferably, the first and second sections are arranged in parallel with the axial direction, and the first and second sections are arranged orthogonally to the third section.
Preferably, the first, second and third sections are stepped in a width direction.
More preferably, the first, second and third sections are tapered from the output side to the input side.
More preferably, the first, second and third sections are stepped in the axial direction both in thickness and width directions.
More preferably, the first, second and third sections are tapered in the axial direction both in the thickness and width directions from the output side to the input side.
Still another aspect of the present invention is a converter for receiving a satellite signal with a dual frequency band having a waveguide of a dual structure with a-first waveguide and a second waveguide coaxially arranged therein. The first and second sections as well first and second probes are arranged between the first and second waveguides, and a third section as well as the third and fourth probes are arranged in the second wave guide.
Preferably, the first and second waveguides have a square or circular cross section in a direction which is orthogonal to an axial direction.
Preferably, the first and second probes in the first waveguide as well as the third and fourth probes in the second waveguide are arranged in a direction orthogonal to the axial direction.
More preferably, the first and second probes arranged in the first waveguide are in parallel with the axial direction, and the third and fourth probes in the second waveguide are in the direction orthogonal to the first and second probes.
More preferably, the second waveguide is formed to protrude backward in the axial direction of the first waveguide, and the third and fourth probes are arranged at the protruding portion of the second waveguide.
More preferably, the third and fourth probes of the second waveguide are connected to a coaxial line, and an outer ground conductor of the coaxial line is a short-circuit means of the first and second probes of the first waveguide.
More preferably, the first and second probes are used for receiving Ku band, and the third and fourth probes are used for receiving Ka band.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.